Right this is one for the tech heads. Am having a rear shock built for next season as the one I used last season is comparable to an Ikea sofa bed so just needed to know what is the eye to eye measurement supposed to be. Am sure Skids,Ghost or one of the other fonts of knowledge can help.
Go for one with an adjustable eye on one end such as Ohlins, Penske and Nitron use. Many of these give 12 to 15 mm of adjustment, Minimum length should be at least 235mm this would then give you the option set to between 235mm to 250mm I think mine hasd ended up at the end of the season set at around 240mm, so probably a good starting point if going for a shock with Non-adjustable length